This routine destroys a mutex object by uninitializing it, and
    should be called when a mutex object is no longer referenced.
    After this routine is called, the Threads Library can reclaim
    internal storage used by the mutex object.

    It is safe to destroy an initialized mutex object that is
    unlocked. However, it is illegal to destroy a locked mutex
    object.

    The results of this routine are unpredictable if the mutex object
    specified in the mutex argument either does not currently exist
    or is not initialized.